Bonding rubber to other surfaces



oct, 2, 1945. H, H. HARKINS A 2,386,112

BONIVDING RUBBER T0 OTHER SURFACES original med July 2, 1938 ATTORNEY Patented Oct. 2, 1945 2,386,112 Flor.

BQNDING RUBBER T OTHER SURFACES Henry H. Harkins, North Providence, R. I., as-

signor to United States Rubber Company, New York, N. Y., a corporation of New Jersey Original application July 217,228. Divided and this 7, 1942, Serial No. 461,211

8 Claims.

This invention relates to adhesive compositions, their preparation, and use, and more particularly v to methods of bonding rubber to metal and the l resulting articles.

composition which is non-gelling in solution and:i

which may therefore be kept for long periods of time under ordinary storage conditions without danger of setting up, i. e., gelling, with attendant loss of adhesive properties. A further object 4is to provide an adhesive composition which will work satisfactorily at temperatures as low as 180-200 F., thus allowing its use in connection with eld Work Where steam pressure for vulcanization is not available. A still mrther Objectis to provide'a method of making a quick drying rubber-to-metal adhesive having the above advantages. Other objects will be apparent from thefollowing description.

The adhesive composition`of the present in-A vention comprises rubber, a soluble reactive phenolic resin, and an oxidizing agent. The term fsoluble is indicative of the solubility of the resin in an organic solvent such as alcohol or benzol. The term reactive refers to those resins which normally are reactive to heat to polymerize to a'. hardened condition. The oxidizing agent may be inorganic, or organic, or b oth may be used. The term oxidizing agent herein refers to those solid oxidizing lagents which are capable of effecting a vulcanizing action on rubber, alone or in combination with other oxidizing agents. The term oxidizing agent herein therefore excludes such as ferrie oxide which is not 'an oxidizing agentA for the purpose of the present invention. Examples of such oxidizing agents include tetrachloroquinone, para-benzoquinone, benzoyl peroxide, polynitroaryl compounds, quinone-imine compounds such as benzoquinone dioxime, etc. The herein useable organic oxidizing agents also function as vulcanizing agents for rubber, and are further exemplied No. 1,918,328 and Fisher French Patent No. 806,500. The preferred inorganic oxidizing agents are those containing oxygen and a multivalent metal, e. g., lead peroxide, manganese` dioxide, mercurio oxide,\lea d chromate, etc. 'Any desired pigment or colormay be added such-as carbon black, etc. In employing such a composition in bonding rubber to metal, it is necessary to first apply to the metal a base coat of phenolic resin, pigmented or not, and then to apply over the base coat the composition containing the oxidizing agent. The rubber stock to be vulcanized to the z, 193s, serial No. application October metal which may be of any desired type or kind, is then applied over the composition containing the oxidizing agent, and the assembly is heated to vulcanize the rubber. The general assembly is shown by the gure of the drawing.

Without the oxidizing agent in the intermediate coating, good adhesion is not obtainable when using reactive resins which are monohydric phenol-aldehyde condensation products. Whereas the polyhydric phenol resins, e. g., heat reac- `tiv'e resorcinol condensation products, may be used Without the oxidizing agents, the results are superiorwith the use of the oxidizing agents. The oxidizing agent alone without the reactive resin does not provide good adhesion. It is believed the oxidizing agent, under the iniuence of heat, cooperates with the reactive resin to vulcanize the rubber, i. e., becomes chemically combined with the rubber, whereas in a heated mixture of rubber and reactive resin alone the rubber .and the resin are merely physically inter- Vmingled and not chemically united. The oxidizing agent modifies the resin in such a way that while it is no longer capable of adhering directlyto'metal, it will adhere to a layer of the unmodied resin itself, which in turn will adhere strongly to metal and other surfaces. Hence the use of the base coat. The mechanism of bonding in Fisher U. S. Patent rubber to metal is as follows: The base cement consisting of heat polymerizable resin, when heated, undergoes polymerization and becomes rmly united.` with the -metal surface. In the intermediate cement, when heated, the rubber becomes vulcanized by the combined action of the resin and the oxidizing agent, and the resin becomes hardened, the resulting composition being strongly adhesive both to the superposed rubber and to the base coat of resin cement. Consequently, a strong bond is obtained between the rubber. and the metal.

' The following data, in which the parts are by weight, shows this vulcanizing phenomenon:

Stocks' X Y Z Pale crepe 100 100 100 Alcohol-soluble Bakelite resin- 8 8 Lead chromate .......Y 8O

subjected to. curing from cresol or butyl' phenol condensed with formaldehyde.

The use of sulphur or sulphur-containing vulcanizing agents may be obviated, if desired, by the present invention in the bonding of rubber to metal. This is sometimes desired in order to avoid sulphur tarnish or dissolution of sulphur from the rubber by liquids. Furthermore, any of the oxidizing agents may be used singly or ln admixture with any of the other oxidizing agents for the purposes of the invention.

The Bakelite type resins have little or no ainity for rubber vulcanized with sulphur, hence an ordinary sulphur-rubber stock when vulcanized in direct contact with a layer of Bakelite provides but poor, if any, adhesion between the vulcanized rubber and Bakelite. By the present invention it has been found that rubber can be securely adhered directly to the Bakelite type resins provided the rubber is vulcanized in contact with the resincontaining mass by non-sulphur organic oxidizing agents which act as vulcanizing agents for rubber such as tetrachloroquinone or other such compounds referred to. If desired, a sulphur-rubber' stock may be applied over the non-sulphur rubber stock, no difficulty attaching to adhering the two rubber stocks.

The following examples are given to illustrate l the invention, the parts being by weight:

Example 1.--A cement made by dissolving 100 parts of a potentially reactive alcohol-soluble phenol-aldehyde resin (Bakelite XR5948) and susf pending 40.parts thermatomic carbon in 100 parts ethyl alcohol is made up, and sand-blasted steel coated with this cement, vand the solvent allowed to evaporate. A stock of the composition Pale crepe 1'00 Tetrachloroquinone 4 Hexamethylene tetramine 2 is sheeted out and rolled on to the steel coated with cement as above. The assemblage is heated in open steam 2 hrs. at 20 lbs. Very good adhesion is obtainable.

In place of tetrachloroquinone, equally good results are obtainable with p-benzoquinone, and p-benzoquinone dioxime.

Example 2.-An alcohol cement of 100 parts of alcohol soluble reactive Bakelite resin (XR-5948) and 40 parts channel black is laid down on the metal surface.

To 100 parts of rubber (pale crepe) on the mill is added 100 parts of a potentially reactive alcohol-soluble phenolaldehyde resin powder (Bakelite Bft-2428), 50 parts channel black, 4 parts tetrachloroquinone, 50 parts lead chromate, and the mass is dissolved in a mixture consisting of equal weights of gasoline (72 B.) and cyclohexyl acetate. This cement is laid down over the metal already coated with the rst cement as given above. The cement coats are allowed to dry thoroughly, then the cement surface moistened with gasoline or other suitable solvent and then the desired vulcanizable rubber stock, the surface of which is also moistened with gasoline or other solvent, is rolled rmly onto the cement layer containing the oxidizing agent. An example of such a rubber stock is as follows: Pale crepe 100; tetrachloroquinone 4; light magnesium oxide 20; magnesium carbonate 10; dibeta naphthyl p-phenylene diamine (anti-oxidant) 1.

The rubber to metal assemblage is heated in open steam Vat lbs. steam pressure for about 2 hrs. The adhesion is uniform and very strong, namely, on the order of 200 lbs. per sq. in., as

assen 12 determined by quantitative adhesion tests approved by the American Society for Testing Materials.

Eample 3.A base cement was prepared in alcohol using 100 parts of alcohol soluble Bakelite resin (XR-5948), 120 parts ferrie oxide, and 500 parts of alcohol. A thin coat of this base cement is applied by,brush or other suitable means to a sand-blasted steel surface.

To 100 parts of rubber on a cold mill is added 100 parts of reactive Bakelite powder (BR-2428) and then as soon as the Bakelite is milled in, the mill is warmed up to melt the Bakelite and disperse it uniformly in the rubber. 50 parts of channel black, 50 parts of lead chromate, and 4 parts of tetrachloroqulnone are now milled in. 182 parts of this stock are dissolved in 540 parts of solvent consisting of equal weights of,gasoline and amyl acetate. This furnishes the intermediatecement.

Two coats of the intermediate cement are applied by brush over the base cement and the cements are allowed to dry thoroughly.

After the cement coats are thoroughly dried, the surface is moistened with gasoline, and a gasoline moistened stock of the following composition is applied: Rubber 100; zinc oxide 5; thermatomic carbon 20; heptaldehyde-aniline. con- 'densate (accelerator) .375.; sulphur 2.5; and an- 4.0 over 100 lbs. per sq.in.

tioxidant 0.5. l

The assemblage is heated in open steam for 60 minutes at 40 lbs. per sq. in. steam pressure. Ad-

hesion tests show that the above stock after vulcanization adheres to the steel with a force of 500 pounds per sq. in. at room temperature. When the rubber to metal sample is heated to 139 C. and held at this temperature until all-parts of the rubber have reached. 130 C. and then the rubber pulled away from the metal, the adhesion is still As distinguished from the monohydric phenol resin or Bakelite resins, the resorcinol resins have been found to exhibit good adhesive properties without the addition of the oxidizing agent in the intermediate cement, although the resorcinol resin' may replace monohydric phenol-aldehyde resin, or be used therewith, in the examples using the oxidizing agent, for the purposes of bonding either 'sulphur or non-sulphur rubber stocks to metal.

Example 4.-200 grams of resorcinol and 70 grams of 37% formaldehyde are heated together in a boiling water bath for 20 minutes. The reaction vessel is then transferred to an oil bath and heated 45 minutes at 15G-155 C. Most of the water is driven off by this heat treatment and a viscous, alcohol-soluble resin is obtained. grams of alcohol are added to the resin to furnish a base cement.

A rubber-resin adhesive-mixture is then made as follows: 15 kgrains of the base cement, 50 grams of 15% .rubber -cement in gasoline, .1 cc. cyclohexanol, and 12 cc. of 4% solution of hexamethylenetetramine in 95% alcohol are mixed together.

A rubber stock to be vulcanized to the metal is as follows: Rubber zinc oxide 5; heptaldehyde aniline condensate .375; sulphur 2.5; antioxidant .5.

Sand-blasted steel is given one coat of the base resin cement and this ls followed by two coats of the rubber-resin cement. After drying, the solid rubber stock is rolled on to the coated steel surface and the assembly heated 2 hrs. in open steam at 20 lbs. pressure.

Both hard .vulcanized and soft vulcanized rubber stocks, and so-called flexible hard rubbers containing Neoprene (polymerized chloroprene) or Vistanex (polymerized isobutylene), may be adhered to metal by means of the present adhesive compositions. When compounded with fats,

taining rubber, a heat-hardened phenol-alde- -hyde resin, and an oxidizing agent selected from the class consisting of tetrachloroquinoneparabenzoquinone, benzoyl peroxide, polynitroaryl waxes or oils, the best results are obtained in 5 compounds, quinone-imines, lead peroxide, manthose rubber stocks compounded with less than 5 parts by weight of the fatty acids, fatty acid soaps, or oils. Y

`The adhesive composition may be used to adhere rubber to a wide variety of metals, in fact '0 to any metal to which Bakelite will adhere, including zinc, steel, tin, brass, bronze, copper, aluminum, lead, Dow metal, etc., as well as to glass,

. wood, etc.

The invention has a variety of uses, one of which is in connection with the manufacture of engravers blankets where a layer `of rubber plus rubberized fabric isv satisfactorily adhered to sheet lead by the use of the present oxidizing agentrubber adhesive compositions as given above. Other uses are in the lining of tanks, conduits, coating, wire, etc.

The term rubber herein refers to natural rub- A bers such as pale crepe, smoked sheet, spray dried lrubbers, etc.

The amount of oxidizing agent may vary within a wide range, ordinarily those amounts which are effective as vulcanizing agents 4for rubber being preferred, in the case of the organic oxidizing agents. For example, suitable proportions of organic oxidizing agent are from 3 to 10%, by weight of the rubber in the adhesive composition; suitable proportions of inorganic oxidizing agents may range from to 200% by weight of the rubber. It is to be understood that in using mixtures of either is required than where either is used alone. The amount of reactive resin in such com--A position may range from 20 to 125%, or more, by weight of the rubber.

Having thus described my invention, what I claim and desire to protect by Letters Patent is:

1. A process of bonding rubber to solidnonrubber surfaces which comprises applying to said surface a base coat consisting essentially of a soluble reactive phenol-aldehyde resin, applying to said base coat and adhesive composition comprising rubber, a soluble reactive phenol-aldehyde resin. and an oxidizing agent selected from the class consisting of tetrachloroquinone, para-benzoquinone. benzoyl peroxide. polynitroaryl compounds. quinone-imlnes, ,lead peroxide, manganese dioxide, mercuric oxide, and lead chromate, and thereover applying' a vulcanizable rubber stock, and heating the assembly. v

2. A process of bonding rubber to metal which comprises applying to the metal surface a base coat consisting essentially of a soluble reactive phenolaldehyde resin, applying to said base coat an adhesive coating comprising rubber, a soluble reactive phenolalqdehyde resin, and an oxidizing agent in an organic solvent said oxidizing agent being selected from the class consisting of tetrachloroquinone, para-benzoquinone, benzoyl peroxide, P0lynitroaryl compounds,V quinone-imines, lead peroxide, manganese dioxide, mercuric oxide, and lead chroxate, and thereover applying a vulcanizable rubber stock, and heating the assembly.

3. A rubber and metal article having a rubber portion bonded to the metal by means of an in-` termediate layer of an adhesive composition con 35 of the organic and inorganic oxidizing agents less 'lo quinone.

ganese dioxide, mercurio oxide, and lead chromate, and a base coat consisting essentially of a heat-hardened phenol-aldehyde re'sin underlying said composition and directly overlying the metal.

4. A laminated article comprising a metal layer, a layer of heat-hardened phenol-aldehyde resin thereon, an intermediate layer of a heathardened composition comprising phenol-aldehyde resin, rubber, and an oxidizing agent superimposed on said resin layer, said oxidizing agent V being selected from the class consisting of tetrachloroquinone, para-benzoquinone, benzoylA peroxide, polynitroaryl compounds, quinone-imines, lead peroxide, manganese dioxide, mercuric oxide,

and lead chromate, and a vulcanized rubber composition superimposed on said intermediate layer, all of said laminae being strongly bonded to one another.

5. A process which comprises bonding rubber to metal by means of an adhesive rubber composition vulcanized in situ by means of the combined action of a soluble reactive phenolaldehyde resin and an oxidizing agent which Y comprises interposing a layer of said composi- 0 tion containing rubber, asoluble reactive phenolaldehyde resin, and an oxidizingagent in an organic solvent intermediatethe rubber and metal and overlying a base coat bontaining a phenolaldehyde resin next to the metal, to form a composite assembly, and afterwards applying heat to the assembly, said oxidizing agent being selected from the class consisting oftetrachloroquinone, para-benzoquinone, benzoyl peroxide, polynitroo aryl compounds, quinone-imines, lead peroxide,

-manganese dioxide, mercurio oxide, and lead chromate.

6. A process for producing articles having a rubber surface securely adhered to a surface of phenolaldehyde resin, which comprises superposon a surface of heat-.hardenable phenolaldehyde resin, a composition containing rubber and a,v non-sulphur-containing organic vulcanizing agent selected from the class consisting of tetrachloroqulnone, para-benzoquinone, benzoyl peroxide, polynitroaryl compounds-and quinoneimines, and heating the assembly to vuicanize the rubber and harden the resin, whereby the rubber becomes securely adhered to the resin surface.

7. A process or securely adhering a rubber composition to a phenol-aldehyde resin which comprises vulcanizing the rubbercomposition while, in contact with` a surface of the resin in heatreactive form, by means of a non-sulphur vorgo ganic oxidizing agent which is capable of vulcanizing the rubber in the presence of heat and selected from the class consisting of tetrachloroquinone, para-benzoquinone, benzoyl peroxide, polynitroaryl compounds, and quinone-imines.

(lli` 8. A process of securely adhering arubber composition to a phenol-aldehyde resin which comprises vulcanizing the rubber composition while, in contact with a surfacel of the resin in heat-reactive form, by means'of a halogenated l, i rmNaY H. HARKINs. 

